Bad news on the X-Men front. Matthew Vaughn, the director of X-Men First Class, has decided not to return for the sequel X-Men: Days of Future Past. He’ll still produce the film and Bryan Singer, the film’s producer and director of the first two X-Men movies, might be stepping in to direct in Vaughn’s stead.

The film already has a release date of July 18, 2014. There’s more below.

Deadline first reported this news, which will be upsetting for First Class fans. They don’t give a reason for Vaughn’s departure, just that “he is pretty picky on projects that he directs.” He famously bowed out of Thor, as well as First Class, before changing his mind on the latter.

As for what he’ll do next, the rumor is he’ll stick at Fox and possibly direct Secret Service, one of Mark Millar’s properties owned by the studio.

Also of note, this is the second time Fox has lost the director of their prominent franchise starter. Rupert Wyatt left Dawn of the Planet of the Apes at about the same time in pre-production. Matt Reeves replaced him.

If Singer does step in, he’ll be obviously be familiar with not only the material, but the superhero genre as well. Some still consider his two X-Men movies to be the cream of the superhero crop (along with Vaughn’s film) and he’s likely learned a bunch from his experience with Superman Returns. If he’s not the studio’s choice, however, who would be a worthy successor?

I must say, after Millar joined 20th Century Fox to oversee their superhero slate, I thought his relationship with Vaughn (the pair worked together on Kick-Ass) was one of the most exciting things about the situation. Surely the coming days will offer more clarification on what happened to push Vaughn off X-Men.